The present invention relates to a composite crucible for melting samples to be analyzed by inductive means.
More or less automated apparatuses are already known for the production, by means of a fusion-dilution process, samples to be analyzed, for example non-metallic samples in form of pearls, destined to be analyzed by a fluorescence with X-rays.
Some of these known apparatuses utilize electrical energy and comprise for this reason fusion means constituted by a vertical induction bobbin excited by a current of high frequency and in the interior of which is placed the crucible containing the sample.
Such an automatic apparatus is described in the French Pat. No. 2,381,303 of the same inventor, which comprises an agitation system for the crucible by means of movement of the bobbin to homogenize the sample during the fusion. Subsequently, thereto the sample is cast into a scoop of solidification, which is preheated either in a temporary manner above the bobbin, or directly on a platform of casting on a second induction bobbin of a structure of a planar spiral.
The fushion crucible, as well as the cooling scoop, are of a material which has the following essential properties: A mechanical resistance at sufficient heat, compatible with the weight of the sample, a good conductivity of electricity and heat, and finally being in the most possible manner inoxidable and chemically inert, even at high temperatures necessary for the melting of the sample.
Considering these requirements on uses generally crucibles and scoops of noble metal, such as platinum or alloys of platinum. Such accessories are very expensive and, even if the scoop has a relatively long useful life, the crucibles have not, but must be replaced after a certain number of fusions depending on the conditions of their utilization. It has been ascertained that certain samples containing metallic phases such as zinc can lead to a rather quick degradation of the crucibles.